Characterization of high voltage spindles and spatial memory in young, mature and aged rats.

EEG was recorded from rats of three age groups, and high voltage spindles (HVS) were measured during waking immobility. Total mean spindling times in 4- (young), 10- (mature) and 22- (aged) month-old rats were 0.3 +/- 0.1, 20.4 +/- 7.4 and 33.4 +/- 14.9 s, respectively. Spatial memory was assessed in these rats using a discrimination version of the Morris water maze. Performance (as measured by number of choice errors) was compared with the extent of HVS activity by characterizing rats as "spindling" if the total average duration of HVS discharges exceeded 5 s, and "non-spindling" if these discharges averaged less than 5 s. Spindling and nonspindling rats had similar performance during training; however, on a 14-day retention trial, spindling rats had a significantly higher mean error score of 2.8 +/- 0.5 compared with 1.2 +/- 0.3 for nonspindling rats (p = 0.011). These results show that spindling activity increases in mature and aged rats, and that HVS discharges may be an electrophysiological change that parallels the progression of brain dysfunction associated with memory impairment.